Floating device providing noise reduction properties

ABSTRACT

The present invention relates to a floating noise reduction system for moving and/or falling fluids, the process for manufacturing of such system and the use of such system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from European patent application No. 10163 520.9-2213 filed on May 21, 2010, all of which is incorporatedherein by reference in its entirety for all purposes.

FIELD OF THE INVENTION

The present invention relates to a floating noise reduction system formoving and/or falling fluids, the process for manufacturing of suchsystem and the use of such system.

BACKGROUND OF THE INVENTION

Falling or dropping and flowing fluid, especially water, is known tocreate significant noise that becomes a health and safety concern forwork personnel and a nuisance for nearby residents. A prominent case isin cooling towers of power plants where costly measures have to be takento reduce the noise. The conditions in cooling towers are among theworst for any sound dampening installation, as there is a permanent highwater impact like from a waterfall moving round in circles. Theresulting force can cause severe damage or at least accelerated fatigueto installations of any kind. Additionally, there has to be appropriate,i.e. highly efficient, drainage as any sound damping installation ofcourse has to work above the water surface situation at the base of thetower. Thus, if a system can work under cooling tower conditions it islikely to work everywhere, e.g. also when applied on flowing fluids.

Some scope in sound attenuating systems has been put on cooling towernoise reduction for a.m. reasons. As the most widespread method, a noiseprotection wall around the base of the cooling tower is 1. costly and 2.only will reduce the noise emitted at ground level but not the noiseescaping through the top opening, other measures had been examined. Oneapproach consists in applying grid-like or mesh-like systems that shoulddisperse the water flow and the noise, subsequently, such as in CN200972335, CN 100533033, CN 2341088 and CN 2453381. The claimed noisereduction of 15-30 dB of the latter could not be reproduced during ourexaminations. Honeycombs as damping elements are mentioned in CN 2823955and CN 1862206, but honeycombs or hollow systems in general arenotorious for creating resonance sound, or “drumming”, of course. Allthe a.m. systems are mainly based on metalwork and/or rigid plastics andthus do not possess material immanent dampening properties. To improvethat situation, JP 8200986 claims the use of a combination of waterpermeable and non-permeable synthetic resin mats, however, also thosematerials are rather rigid and the drainage properties—despite theclaimed drainage ridges—are poor, leading to water agglomeration on topof the mat which will increase the noise level again. CN 2169107mentions damping mats and particles; however, the claimed system is notable to provide sufficient structural integrity for the application.Another approach is focussing on plate systems where the platesthemselves are supported by a damping device and also disperse water,such as in CN 201003910, CN 201302391, CN 201302392, CN 201302393, CN201184670, CN 1945190 (all describing combinations of rotating and fixedplates, partially combined with pipe systems), CN 201311202 (microporousplates), CN 2821500 (plates, rings and surface structures as known fromacoustic indoor systems), JP 56049898 (complex metalwork with dampinginlays). Other systems described in the literature are: CN 2447710 andCN 2438075 (use of floating balls) and CH 451216, DE 3009193, DE1501391, DE 2508122, EP 1500891, SU 989292. The latter documents, aswell as a publication (M. Krus et al: Latest developments on noisereduction of industrial induced draft cooling towers, Veenendaal, 2001,pp 33-38) all mainly refer to systems consisting of floating deviceswhich are supporting or carrying the damping system, consisting ofmat-like structures, means, some elasticity or flexibility has beenacknowledged to be beneficial for sound dampening; JP 58033621 at lastmentions that “soft cover” may reduce falling water noise (for sluicedoors). However, those systems are not consequently using the potentialof elastic dampening and exhibit deficiencies in floating properties aswell as in drainage performance; and some systems again are sensitive tomechanical impact.

SUMMARY OF THE INVENTION

A major object of the present invention thus is to provide a floatingnoise reduction system or material combination not showing the abovementioned deficiencies but exhibiting a significant and sustainablelevel of noise reduction over all concerned frequencies and showing anadditional drainage effect and high mechanical wear resistance.

Surprisingly, it is found that such system or material not showing theabove mentioned disadvantages can be made from a combination of expandedelastic material with a floating mechanical support made from expandedpolymer.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings,

FIG. 1 schematically illustrates the composition of claimed system,

FIG. 2 schematically illustrates the skeleton (reticulated) structure,

FIG. 3 schematically illustrates the damping of flowing or falling fluidor waves,

FIG. 4 schematically illustrates the possible surface structures fordrainage and absorption for layers (A) and (B),

FIG. 5 schematically illustrates the test layout for falling water noisedetection, and

FIG. 6 shows the frequencies being damped by claimed materials: ⅓ octaveband spectra resulting from falling water test.

DETAILED DESCRIPTION OF THE INVENTION

The claimed material comprises at least one layer (A) of expandedpolymer based material with open cell (open porosity) structure (FIG.1). The polymer based material of (A) can be expanded from an elastomerand/or thermoplastic elastomer (TPE) and/or thermoplastic and/orthermoset based polymer mixture, or combinations thereof, and canoptionally be crosslinked to improve mechanical (e.g. compression set)and wear properties. Preferred are polymer based materials providingelasticity to (A), either by elastic properties provided by the polymeritself (e.g. for elastomers and TPEs) or by respectively thin, thusflexible expanded structures, or by a combination of both. The polymerbased material is expanded by physical and/or chemical expansion agentsto an open cell sponge or reticulated (skeleton) structure, depending onthe required damping and drainage properties. Preferred is a reticulated(skeleton) structure where the polymer based cell walls are reduced tocolumns showing a diameter thinner than the average cell diameter (seeFIG. 2). The polymer based material can be a mixture or compound thatmay contain fillers, such as oxides, carbonates, hydroxides, carbonblacks, recycled (ground) rubber, other recycled polymer materials,fibres etc., and additives, such as flame retardants, biocides,plasticizers, stabilizers, colours etc., of any kind in any ratio. Thepolymer base mixture may be crosslinked by any applicable mean ofcrosslinking, such as sulphur, peroxide, radiation, bisphenolics, metaloxides, polycondensation etc. (A) can show various densities, preferredare densities lower than typical fluids, e.g. lower than 700 kg/m3, toprevent sinking even when fully soaked. Especially preferred aredensities lower than 300 kg/m3. It is easily feasible to use variouscombinations of polymer based compounds and various combinations oflayers (A) made thereof. (A) will quickly absorb the falling or flowingfluid, disperse its impulse into smaller drops and in parallel willdisperse the resulting impact energy transversally into the matrix of(A). This dispersion will continue through the open cell structure andinto layer (B) and finally will lead to noise absorption within theclaimed material and transmission of remaining noise into the fluidunderneath when damping falling fluid, or into the medium above oroutside when damping flowing fluid, or into a lateral medium whendamping e.g. waves (see FIG. 3). Meanwhile the absorbed fluid itselfwill be silently drained through (A) and (B) to the fluid underneath orinto the medium above or drained laterally. Layer (B) thus not only actsas floating and draining part of the system, but supports the noisereduction by interaction with (A) and by providing further potential fordamping additional frequencies. (A) can be of flat surface to thefalling fluid, or it can be structured to alter theabsorption/dispersion properties, and it can be equipped with e.g. pinholes for better drainage. (A) can also be structured on its face to (B)for same reason, e.g. for drainage or sound decoupling purposes (seeFIG. 4). Preferred materials for the manufacturing of (A) areelastomers, such as NR, IR, SBR, NBR, CR, IIR, EPM, EPDM, Q, etc.,thermoplastic elastomers, such as TPP, TPV, TPU, SAN, SEBS etc., PIR/PURor polyurethanes, especially reticulated polyurethanes, polyesters,phenolic and melamine based compounds.

The claimed system comprises at least one layer (B) of expanded polymerbased material different or same as for (A) with either open or closedcell structure (FIG. 1). The polymer based material of (B) can beexpanded from an elastomer and/or thermoplastic elastomer (TPE) and/orthermoplastic and/or thermoset based polymer mixture, or combinationsthereof, and can optionally be crosslinked to improve mechanical (e.g.impact strength) and wear properties. Preferred are polymer basedmaterials providing structural integrity to (B) to prevent breaking orwarping of the system. The polymer based material is expanded byphysical and/or chemical expansion agents to an open cell sponge orclosed cell foam, depending on the required mechanical, damping anddrainage properties. Preferred is a minimum 50% closed cell structure,especially preferred are at least 70% closed cells to prevent soakingand saturation with fluid. The polymer based material can be a mixtureor compound that may contain fillers, such as oxides, carbonates,hydroxides, carbon blacks, recycled (ground) rubber, other recycledpolymer materials, fibres etc., and additives, such as flame retardants,biocides, plasticizers, stabilizers, colours etc., of any kind in anyratio. The polymer base mixture may be crosslinked by any applicablemean of crosslinking, such as sulphur, peroxide, radiation,bisphenolics, metal oxides, polycondensation etc. (B) can show variousdensities, preferred are densities significantly lower than typicalfluids, e.g. lower than 500 kg/m3, especially preferred are densitieslower than 200 kg/m3. It is easily feasible to use various combinationsof polymer based compounds and various combinations of layers (B) madethereof. (B) comprises a structure to ensure good drainage properties as(B) is responsible to draw the fluid away from (A) into the fluidunderneath. This structure can comprise pin holes that can be applied ina wide variety of size and pattern and combinations. The structure canalso comprise ridges of any shape in any combination (e.g. triangular,sinus-like, rectangular, trapezoidal etc.) that can be applied on one orboth surfaces of (B) (see FIG. 4). (B) can be fixed to (A) by mechanicalmeans, or chemically by bonding, or by a combination of both. Layers (A)and (B)—and optionally (C)—can be brought together directly byco-forming, e.g. by co-extrusion and/or co-moulding and/or lamination,and/or can be connected after giving shape to them. The connection canbe achieved by adhesives, e.g. one or two part silicone, polyurethane,acrylate, chloroprene, contact adhesives or hot melts or any combinationthereof. Or the connection can be achieved by direct melting or weldingthe two materials together, such as by UHF welding or the like. Thepreferred final form is a mat or tile like multilayer compound system.The tiles can easily be cut and shaped to fit any geometry of the fluidbasin or fluid track to float on. Preferred materials for themanufacturing of (B) are elastomers, such as NR, IR, SBR, NBR, CR, IIR,EPM, EPDM, Q, etc., thermoplastic elastomers, such as TPP, TPV, TPU,SAN, SEBS etc., PIR/PUR or polyurethanes, polyesters, phenolic andmelamine based compounds. Especially preferred are compounds providinghigh impact strength, such as polyalkylidene terephthalates.

The claimed material furthermore may comprise one or more additionallayers (C) within and/or between layers (A) and/or (B) that may provideadditional drainage and/or damping and/or other properties, such aspreferably reinforcement, impact resistance etc. The layers (C) can e.g.comprise fibres, e.g. as mesh, or nonwoven, wire mesh, resin sheet etc.of any kind; see FIG. 1.

The claimed material furthermore may comprise a link system (D) thatconnects individual pieces, e.g. tiles, comprising layers (A), (B), andoptionally (C) together, but still leaving room to move and float. (D)can comprise metalwork, woven bands, elastic links etc., or acombination thereof. (D) is fixed either into layer (B)/(C)—as thestructurally toughest ones—or into the system, i.e. (B), from underneathor above or by a combination of both methods. Care has to be taken that(D) will not negatively influence the floating properties (weight) andthe flexibility of the whole system. Cardan joints or axle bearing basedlinks or other flexible linking methods are therefore preferred. Anaccordingly strong layer (C) between (A) and (B) can also take the partof (D) if the pieces of (A) and (B) are connected onto (C) keeping somedistance between the respective tiles. However, a connection system (D)is preferred where individual tiles can be easily exchanged, e.g. formaintenance purposes.

It is a prominent advantage of the claimed material that it is providingexcellent damping together with draining effect due to its compositionand structure and that it additionally shows built-in anti-fatigueproperties due to its composition, allowing long-term use even underharsh conditions.

A further advantage of the claimed material is the possibility to adaptits properties to the desired property profile (concerning mechanics,damping/absorption, fluid intake, hydrophilic or hydrophobic character,porosity etc.) This can be achieved by modifying the expansion agent(s),the expansion process and the polymer base material composition, as wellas the density, and, if required, the crosslinking system(s). Thematerial thus can be altered to damp/absorb from high to low frequenciesor frequency bands (see FIG. 6), and it can be used in contact with abroad variety of fluids, including aggressive and/or hot or cold ones.

Another basic advantage of the claimed material is the fact that itsnoise reduction properties are very constant over a wide temperaturerange leading to the fact that its performance remains unchanged nomatter if it is used in summer or wintertime.

It is a further important advantage of the claimed material that it willreduce both the ground level noise as well as the top level noise atcooling towers (see table 1 and FIG. 6), rendering noise protectionwalls obsolete.

It is another important advantage of the claimed material that it can beapplied for noise reduction both of falling/dropping and flowing fluids.

It is another advantage of the claimed material that it is environmentalfriendly as it does not comprise or release harmful substances, does notaffect water or soil or nature in general and as it is recyclable byseparating the layers and then grinding or melting them individually.

A resulting advantage of the material is the fact that it can be blendedor filled with or can contain scrapped or recycled material of the samekind to a very high extent not losing relevant properties significantly,which is especially the case for (B) and (C).

It is another advantage of the claimed material that its expandedstructure provides insulation properties, thus, it can be beneficial forkeeping fluids warm or cold in addition to the damping properties.

It is a prominent advantage of the claimed material that it can beproduced in an economic way in automatic or semi-automatic shapingprocess, e.g. by moulding, extrusion and other shaping methods. It showsversatility in possibilities of manufacturing and application. It can beextruded, co-extruded, laminated, moulded, co-moulded etc. as singleitem or multilayer already and thus it can be applied in almostunrestricted form.

It is a further advantage of the claimed material that it can betransformed and given shape by standard methods being widespread in theindustry and that it does not require specialized equipment.

It is another advantage of the claimed material for the application thatit is long-lasting and durable, however, easy to change in case ofmaintenance and thus will reduce running costs for the user.

EXAMPLES

Preparation of Test Samples

1. Floating layer (B): an extruded, expanded and cut PET board of 25 mmthickness and 1000×1000 mm width (ArmaStruct®, Armacell, Münster,Germany) was coated with a silicone adhesive layer (ELASTOSIL® R plus4700, Wacker Chemie, München, Germany) to give the floating part of thesystem. A sinus shape ridge structure (distance peak to peak of 35 mm)was applied to one surface by thermoforming embossing and pin holes of20 mm diameter were drilled into the board in a distance of 80 mm.

2. Sponge like open cell absorbing layer (A): A rubber compound(Armaprene® N H, Armacell, Münster, Germany) was extruded, expanded andcut to an open cell foam mat of 25 mm thickness and 1000×1000 mm widthand then laminated onto the plain surface of (B) as single or doublelayer by heating the composite up to 120° C. in a hot air oven, usingthe a.m. adhesive.

3. Skeleton structure open cell absorbing layer (A): A reticulatedpolyurethane foam mat of the type 80 poles per inch (SIF®, United Foam,Grand Rapids, U.S.A.) of 25 mm thickness and 1000×1000 mm width waslaminated onto the plain surface of (B) as single or double layer byheating the composite up to 120° C. in a hot air oven, using the a.m.adhesive.

Experimental Setup

The experiments were carried out on test equipment proposed anddeveloped by the University of Bradford, UK (Prof K. Horoshenkov). Thesetup (see FIG. 5) comprised of a large underfloor concrete water tank.The tank was 2.5 m deep, 1.8 m wide and 2.35 m long and was able to holdapproximately 8 m3 of water. The water was discharged onto theunderfloor tank from a perforated water tank mounted above. Theperforated water tank was made of PVC and its dimensions were 0.55 mwide×0.55 m long×0.2 m deep. In order to simulate the discharge typicalto that measured in a cooling tower the perforated water tank had 243holes all 1 mm diameter wide drilled in a 5 mm thick base, the spacingbetween the perforations was approximately 26 mm. The size of theperforations was chosen in accordance with the ISO 140, Part 18 (2006)and corresponds to that required to generate heavy rain. The perforatedwater tank was calibrated to deliver 5 m3/m2/hr discharge. This requireda water supply at the rate of 20.8 litres per min. The calibration wascarried out by using a standard flow meter and by weighing the amount ofwater discharged from the hose pipe over 15 sec intervals. It requiredthe PVC water tank to be filled with 180 mm of water to achieve theequilibrium between the water pick-up and runoff.

The absorber foam samples (A) were tested in single and double layerconfigurations placed on top of the floating layer (B) by adhesion asdescribed above. The distance between the top surface of the top foamlayer and the bottom of the perforated water tank was kept 2 m in allthe experiments to ensure the same terminal velocity of the waterdroplets. The following items of equipment were used for sound recordingand analysis:

(i) one PC with WinMLS 2004 build 1.07E data acquisition and spectrumanalysis software and 8-channel Marc-8 professional sound card.

(ii) four calibrated Bruel and Kjaer microphones, ½″ type 4188.

(iii) one 4-channel B & K Nexus conditioning amplifier type-2693 set at1V/Pa.

The audio channels were calibrated to 94 dB using a standard B&Kmicrophone calibrator (Type 4230, no: 1670589). The ⅓-octave soundpressure level spectra were measured on the four channels and used tocalculate the mean ⅓-otave level spectrum and the broadband soundpressure level (see FIG. 6). The lateral positions of the fourmicrophones in the underfloor water tank are shown in FIG. 5. Themicrophones were suspended on cables 0.8 m below the bottom of theperforated water tank. The level of ambient noise in the laboratory wasvery low and signal to noise ratio of better than 20 dB was ensuredthroughout the tests.

Results

Table 1 shows the good damping properties of already a standard spongestructure open cell material. The noise reduction effect even gets muchbetter when very open cell (“skeleton structure”) material is applied.Another incremental improvement can be found in a combination of both.

TABLE 1 Falling water test: noise reduction of open cell materials (A) -SpC = Sponge-like open cell structure; SkC = Skeleton-like open cellstructure - in 25 and 50 mm thickness applied on a given layer of (B) incomparison with the unarmed water surface (all innovative examples).Avg. sound pressure Type of layer (A) level (dB) Noise reduction by dBSpC foam 25 mm 68.4 8.2 SpC foam 50 mm 67.6 9.0 SkC foam 25 mm 54.5 22.1SkC foam 50 mm 54.5 22.1 SkC + SpC (25 + 25 mm) 52.6 24.0 No damping76.6 n.a.

The frequencies being damped or absorbed also give an indication aboutthe performance of the materials and material combinations. FIG. 6 showsthe ⅓ octave band spectra for the materials of table 1 and proves thatthe skeleton like structure also has advantages in damping a broaderrange of frequencies (the sponge like structure tends to boom at lowfrequencies), however, it can be found, too, that a combination of bothmaterials is performing slightly better.

1-9. (canceled)
 10. A system for noise reduction of moving fluids,including waves, comprising at least one open cell absorption layer andat least one mixed cell absorption and drainage layer wherein bothlayers, the open cell and the mixed cell layer are obtained fromexpanded polymer based material showing a total average density of lessthan 1000 kg/m³.
 11. The system according to claim 10 wherein the mixedcell layer contains at least 70% closed cells and shows a density ofless than 700 kg/m³.
 12. The system according to claim 10 wherein theopen cell layer shows a density of less than 500 kg/m³.
 13. The systemaccording to claim 10 wherein the open cell layer comprises reticulatedfoam.
 14. The system according to claim 13 wherein the reticulated foamshows a cell structure of 10 to 300 pores per inch, wherein the polymerbased material cell wall columns show a diameter thinner than theaverage cell diameter.
 15. The system according to claim 10 wherein themixed cell layer comprises at least one of polyolefin or polyalkylideneterephthalate.
 16. The system according to claim 10 where at least oneof drainage holes or ridge structures are applied in at least one of themixed cell layer or the open cell layer.
 17. A process for manufacturingthe material according to claim 10 comprising forming said layers in atleast one of a moulding and adhesion process, continuous extrusionprocess or co-lamination, followed by applying said system to a desiredstructure.
 18. A system according to claim 10, for noise reduction ofmoving fluids, flowing fluids, falling fluids or fluids creating waves.19. The system of claim 11 wherein the mixed cell layer density is lessthan 300 kg/m³.
 20. The system of claim 12 wherein the open cell layerdensity is less than 200 kg/m³.
 21. The system of claim 14 wherein saidcell structure is 20 to 120 pores per inch.
 22. The system of claim 18,for noise reduction of water channels, water ponds, in cooling towers orat shores.